X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=5fd016a6db59500df25c5e2122d9ea8845c08e7a;hp=7875f0345f3d9d9f4c0268b7d613689f7cd85c7e;hb=04407e35d67959b2e9011aa6aff43e2bb632b189;hpb=4d647428d8f6b02a404e6b7fda5dbbf17090f271

diff --git a/src/search.cpp b/src/search.cpp
index 7875f034..5fd016a6 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -577,6 +577,17 @@ namespace {
         beta = std::min(mate_in(ss->ply+1), beta);
         if (alpha >= beta)
             return alpha;
+
+        // Check if there exists a move which draws by repetition, or an alternative
+        // earlier move to this position.
+        if (   pos.rule50_count() >= 3
+            && alpha < VALUE_DRAW
+            && pos.has_game_cycle(ss->ply))
+        {
+            alpha = VALUE_DRAW;
+            if (alpha >= beta)
+                return alpha;
+        }
     }
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
@@ -734,10 +745,10 @@ namespace {
     // Step 9. Null move search with verification search (~40 Elo)
     if (   !PvNode
         && (ss-1)->currentMove != MOVE_NULL
-        && (ss-1)->statScore < 30000
+        && (ss-1)->statScore < 22500
         &&  eval >= beta
         &&  ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
-        && !ss->excludedMove
+        && !excludedMove
         &&  pos.non_pawn_material(pos.side_to_move())
         && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))
     {
@@ -1106,7 +1117,7 @@ moves_loop: // When in check, search starts from here
               else
               {
                   assert(value >= beta); // Fail high
-                  ss->statScore = std::max(ss->statScore, 0);
+                  ss->statScore = 0;
                   break;
               }
           }
@@ -1153,7 +1164,7 @@ moves_loop: // When in check, search starts from here
             update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
     }
     // Bonus for prior countermove that caused the fail low
-    else if (    depth >= 3 * ONE_PLY
+    else if (   (depth >= 3 * ONE_PLY || PvNode)
              && !pos.captured_piece()
              && is_ok((ss-1)->currentMove))
         update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));